In the siting and planning of large scale construction projects, such as dams, buildings, offshore drilling platforms, nuclear power plants, and the like, it is necessary to ascertain the nature and strength of the earthen formation which will support the construction project. Typically, core samples of the subsurface earthen formation are obtained, and subjected to testing to discover critically important factors such as yield strength, ambient stress patterns, elasticity, plasticity, etc., of the earth at the potential construction site. These factors are generally determined through the use of instruments known in the prior art. Such instruments generally operate by subjecting the core sample to an axial compressive load while measuring the strain created by the load, the load factor being increased until the sample fails. This form of test is generally reliable in determining the strength of the subsoil formation under the static load of the project to be built.
However, in many siting situations the dynamic situation is not static, but is subject to rapidly varying load factors. This may occur in earthquake zones, where rapid lateral acceleration not only alters the vertical equilibrium, but also may significantly change the strength of the subsoil formation. Likewise, offshore platforms are subject to wave action creating an added lateral force vector which varies greatly in direction and magnitude. These lateral forces must be taken into account when a construction project is planned to assure the survival of the project.
There is a deficiency in the prior art in instruments which can test subsoil samples in dynamically varying conditions as well as static load conditions. Prior art instruments have tended to introduce large errors into the test results, due in part to poor mounting of the sample which results in erroneous strain measurements. A further problem in the presence of excessive friction in the mounting of the sample for lateral loading in addition to axial compression. The frictional effects results in data which is open to question and is often not reproducible in successive tests. When the data is not reliable it is dangerous to use it to make decisions involving expensive and large scale projects.
Furthermore, the prior art instruments are deficient in that they require a great amount of time to prepare and mount each sample in the instrument. Thus each testing procedure may require a long time, and the testing of a large number of core samples may be prohibitively lengthy and costly. Also, the preparation may necessitate rehydration of the sample, and this task has proven to be problematical in prior art setups.